LM3150: EMC conducted emission support

Hello Allen,

Need to place capacitance on the left side of the input inductor, L7, not the right side.  Noise source you are filtering is on the right of the input inductor.  Also, I don't see any input filter damping. please refer to the document below.  the damping capacitor needs to be placed on the right side of the inductor L7.

Input Filter Design for Switching Power Supplies (ti.com)

Hope this helps.

David.

Hello Allen,

You could short out L7 and the emissions will get worse, alternatively you can place a capacitor left side of L7 and observe that various difference values of capacitance will give you various degrees of attenuation in the EMC plot.

Regarding layout guidelines, there are some in the datasheet.  To answer your question about SGND specifically, yes, suggest tying ground side of all small signal components to an SGND polygon pour and tying the polygon pour back to SGND pin.  Then tie the SGND pin to the DAP of the device.  PGND will have its own polygon pour that is tied back to PGND pin and the PGND pin is connected to the DAP also.  You can place multiple Vias near the SGND, PGND pins and place a few on the DAP.  Vias will be tied to a solid GND layer directly beneath the top layer that the device and power stage are mounted on.

Please see rough draft of a complete layout/floorplan below, for the LM3150.  hope this helps.

David.

Hello Allen,

If you do emissions testing without L7, the EMI will be worse, suggest using L7 with the recommendations given above.  Thanks.

David.